Sand casting has long been used to form cast metal parts such as pistons, crankshafts, connecting rods and engine blocks. Although sand casting is a generally economical method of producing cast metal parts, it is typically considered labor intensive, particularly insofar as removing the mold sand from the cast parts. More particularly, whether manual or mechanized procedures are used for scraping, brushing and/or abrading the mold sand from the cast parts, it is generally held that removing such sand from a casting is one of the most expensive aspects of foundry processing. Conventional methods in which operators blow the sand off the cast parts with pressurized air have been known to require one-third of the total energy requirement of making a cast part. Before air-blasting, the cast part must also be cooled for handling. Later, the cast part will have to be reheated for heat treatment, if heat treatment is desired. In the practice of this prior art method, laborers use shop air sources with a nozzle to individually blow the loose sand from the sand-casted metal parts. This poses three particular problems: (1) the blow-off is labor intensive; (2) very high noise levels due to the blow-off operation render OSHA compliance difficult in order to avoid hearing loss of the laborers; and (3) time requirements are too high because the part must be cooled before it is blown off, requiring re-heating at a later time to perform heat treatment. Furthermore, the previous method was inefficient because the residual heat left over from the casting process if not utilized for the heat treatment process because the laborers cannot handle metal parts at 1400.degree.-1700.degree. F. in order to blow-off the clinging sand.
An additional expense associated with sand casting is the cost of reclaiming the foundry sand. That is, once the sand has been removed from the cast parts, the sand, which is typically in the form of sand clumps, must be further reduced to individual sand grains. The grains must then be cleaned and screened before they may be used to form a new mold.
Once a typical sand casting has been cleaned, it is often subjected to additional processing such as machining and heat treating. For heat treating, the cast part, which has cooled to room temperature, is reheated to a predetermined elevated temperature for a predetermined length of time to achieve certain desired properties in the treated part. One such treatment is known as austempering wherein the cast parts are tempered to improve their toughness. This type of heat treatment is not only time consuming, it is also relatively expensive and is often accomplished outside the foundry in independent heat treatment facilities.
Accordingly, a need exists for an efficient and economical method and apparatus for removing sand from metal sand castings and the like and for allowing simultaneous reclamation, cleaning and screening of the sand for reuse. A further need exists for a more economical method and apparatus for heat treating metal sand castings within the foundry.